The Best Way to Divide and Replant Iris

Regular division helps prevent iris diseases caused by overcrowding.

The iris family (Iris spp.) includes more than 300 species, but the most common garden varieties all feature flowers with drooping outer petals and upright inner petals. Most irises grow in U.S. Department of Agriculture plant hardiness zones 3 to 9, but hardiness depends on the specific variety. These perennials require minimal maintenance, but they do benefit from root division every three to five years to minimize overcrowding. Divide in late summer or early fall, after the plants are done flowering.

Plant and Tool Preparation

Disinfecting all your tools before you begin provides the best defense against iris diseases later. Soak shears and any other tools in a 1 part bleach to 9 parts water solution for 30 minutes. After you disinfect the tools, cut back the iris leaves to a third of their height. If the iris has any dead or damaged leaves, you can prune these back to their base. Dip the shears in the bleach solution after cutting through a damaged leaf or when moving to other plants to further minimize the spread of disease organisms.

Digging Method

Iris rhizomes can spread out farther than the visible leaf crown, so begin digging about 6 inches out from the base of the outermost leaves. Dig carefully so you don't accidentally cut or gouge an iris root. Slide the trowel beneath the rhizomes and lift them out of the soil. Set them down so the leaves aren't broken or bent. Brush off as much soil from the rhizomes as possible, but avoid wetting them -- wet rhizomes are more prone to rot and disease.

Root Division

An iris rhizome resembles a swollen tuber, with narrow waist segments spaced irregularly down its length. Small rootlets trail from the bottom of the tuber, while the leaf fans emerge from the top. Examine the rhizomes and trim off any soft, rotten or diseased-looking sections with a knife, disinfecting after every cut. Slice apart the remaining healthy rhizomes so each division has a leaf fan and two or more healthy rootlets attached.

Successful Transplanting

Well-drained garden beds in full sunlight are the best planting locations for the divided irises. Plant the divisions so their tops are just below soil level. Planting too deeply increases the dangers of rhizome rot. Plant the rhizomes in groups of three in a loose circle, with the rhizomes orientated so the leaves fan out and away from the center of the grouping. Leave 12 to 24 inches of space between each grouping. Water the rhizomes after planting just enough to moisten the soil. Once established, irises rarely require additional watering.

About the Author

Jenny Harrington has been a freelance writer since 2006. Her published articles have appeared in various print and online publications. Previously, she owned her own business, selling handmade items online, wholesale and at crafts fairs. Harrington's specialties include small business information, crafting, decorating and gardening.